Feed screw



Nov.` l1, 1941.4 F. s. FRANKLAND FEED SCREW Filed Nov. 6, 1939 Humm .D 2 3x7 25H7 1N VENTOR.

Q MY.

Patented Nov. 11, 1941 FEED SCREW Forrest S. Frankland, Pittsburgh, Pa., assigner to The Carpenter Heating t Stoker Company, Cleveland, Ohio, a corporation of Ohio Application November 6, 1939, Serial No. '303,071

(Cl. ISS-217) 3 Claims.

This invention relates to apparatus of the type comprising a hopper or retort into which material is continuously fed by a rotating screw, and relates in one aspect to an improved construction of feed screw.

The principal use of my invention is in its application to coal stokers for furnaces, and will hereinafter be described as applied to that use, but as will become apparent hereinafter, it may be applied to other uses and is not to be considered as strictly limited to its application to coal stokers.

In Stoker practice, fresh coal is fed to the retort or fire box of the furnace through a tube or conduit by means of a screw axially disposed in the conduit and rotatable therein and projecting beyond the end of the conduit into the retort.

With screws such as have heretofore been employed, the screw tends to pack the coal in the retort and such packing at times becomes so rigid as to stop the rotation of the screw, and causes the screw to be broken by the tortional power applied thereto to rotate it, Also, with screws as heretofore provided, the coal is not uniformly distributed in the retort when fed thereinto by the screw.

Furthermore when the firebox or retort is of the underfed type in which the coal is fed into the lower part of the retort and moves upwardly into the combustion zone and out in the form of ash, the lack of uniformity in the distribution of the coal resulting from the use of prior screws causes a non-uniform rire.

It is with these objections to prior stokers of this type in mind that the present invention has been made, and the primary object thereof is to provide generally an improved construction of feed screw and retort, dimensionally and structurally related to each other so that packing of the coal is prevented, and uniform distribution thereof throughout the retort and uniform upward feeding thereof out of the retort into the fire zone, is effected in an improved manner.

Other objects are:

To provide generally an improved construction of discrete material feeding screw;

To provide an improved method of constructing a feed screw dimensionally proportioned to the retort or hopper or the like into which it feeds material, to effect prevention of packing of the material in the retort, and to effect improved uniformity of feeding of the material through the hopper by the screw;

To provide generally an improved construction i of feed screw for feeding material into a hopper retort or the like;

To provide generally an improved stoker screw and retort or fire box co-operating with each other in an improved manner.

Other objects will be apparent to those skilled in the art to which my invention appertains.

My invention is fully disclosed in the following description, taken in connection with the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of a stoker retort or re box and a feed screw associated therewith embodying my invention in a preferred form;

Fig. 2 is a view of the screw illustrated in Fig. 1, the view being taken in a direction at right angles to the direction from which the screw of Fig. 1 is viewed.

Referring to the drawing I have shown generally at l, a stoker retort or fire box having a bottom wall 2, and end walls 3 and 4. At 5 is a feed conduit, communicating with the interior of the retort.

At 6 is a feed screw disposed axially in the conduit 5 and extending into or projecting through the retort I. The outer end of the vscrew 6 is provided with a cylindrical bearing portion 1, rotatably supported in a bearing 8 in the end wall 4, which bearing may be hushed, as shown, if desired. The opposite end of the screw 6 and of vthe conduit 5 are not shown being broken off to simplify the drawing, but it is to be understood that the conduit 5 communicates with a coal supply hopper from which coal is supplied to the conduit, and the corresponding end of the screw 6 communicates with said hopper, and power means is provided to rotate the screw 6 in the direction of the arrow 9 to feed coal from the hopper into the conduit 5, and propel it therethrough toward and into the retort I.

In this connection, it will be understood that the end of the screw 6, not shown, may be rotatably supported in a suitable bearing or it may be allowed to float in the conduit 5, rotatably resting upon the lower inner side of the conduit 5.

Such a coal supply hopper and conduit and screw portion to feed coal into and through the conduit 5 are'well known in this art and it is deemed unnecessary to complicate this disclosure by illustrating and describing the same, inasmuch as these parts do not constitute any essential part of the present invention.

The conduit 5 is preferably so related to the retort l that the lower inner wall I0 of the retort l is in effect a continuation of the inner lower wall II ofthe conduit 5, whereby the thread of the screw, to be referred to, sweeping over the wall II to propel coal therealong will continue l to sweep over the wall I in a similar manner.

tuyre devices for supplying air inwardly forV combustion purposes. Such devices, being well known, have been illustrated fragmentarily. Means for providing forced draft by a supply of air under pressure may be provided and this also being well known in the art has' been omitted for simplicity of disclosure.

Coming now to parts more particularly involved in the embodiment of my invention, it` will be` understood that the end walls 3 and 4, and more particularly the inner wall faces I5 and I 6 thereof will be spaced apart longitudinally a distance determined by the output capacity desire-d for the stoker as a whole. The`A transverse width of the retort between the walls I3, onel of vwhich is shownymay for convenienceA of manufacture be the same for differentretortaand to provide different capacities, the distance between the walls I5 and I6 may be different indifferent stokers.` As will become clear as this description pro-1` ceedS, I provide, on thatpart of the screw within the retort, a rdiscontinuous thread, Vpartv of which is reversed lwith respect to the main part'of the thread propelling the coal forwardly through the conduit'5, and I have provided a method by which* this discontinuous', partly` reversed thread, may

l be. constructedrto-carry out theprinciples of my invention, in accordance with the different lengths of the retort: between the walls' I5 and I6,

j which distance I have represented in the drawing@ 3 atzy'.

The screwl comprises in generalv a .central or axial shaft portion I'I, and, in the partA thereof withinthe conduit 5, the shaft I'I has ahelical forward' thread I8 thereon of suitable pitch which has beenA determined by practice and which maybe 1 the pitch commonly employed-- in priorl stoker screws.

The thread or main flight I8v continues into the retort'l beyond the rearward wall face I5 for ap-' l proximately one complete revolution, and there terminates, this revolution ofthe thread being l indicated by a. Ashort length yof the shaft represented by b is bare, that is to say, has no thread, and this length of the shaft; for stokers of the? most common size `or' capacity may beabout an inch and one eighth longitudinally of the shaft. l At the end of this bare lengthof shaft, the thread `begins again at a point'l80 around the shaft from the point at which thefthread I8 terminates,

and the thread proceeds inl reverse direction as shown at` I9,A continuing for. approximately a half revolution, this part orv flight of the thread be- `ingrepresented at c;

,The reverse ight lI!! of the thread is joined to4 afforwardv flight 20, in a relatively sharp edge 2'I, and the forward flight 2U continues` for approximately one completerevolution, being reprelsented by d. This flight '20 is followed by`another bare part r of the shaft, represented by e which may be the `same as thatrepresented at b, and then at a lpoint, preferably 180 around the shaft, another jreverse night 22 begins,'continuin'g for approxi- Imately a half v revolution where', at a relatively As will now be apparent, the extent of the bare partsof the shaft b', e and h., as well as the extent of the forward flights a, d and g and the extent of the reverse flights c, f and i, can be varied considerably in the absolute sense as well as relative to each other.

In the operation of the screw and retort above described and as illustrated, the feed of the coal by the main ight I8 is opposed by the reverse Hight I9; and the forward feed by the forward flight 20 is opposed by the reverse flight 22; and the forward feed by the forward flight 24 is opposed by the reverse fiight 25. 'I'he reverse flights insure that there will be no packing of the coal against the end wall I6, or anywhere in the retort. The forward flights insure that the coal will be fed continuously into the retort. The: net result therefore is that the coal is fed into the retort and upwardly therethrough, and in action the coal is constantly agitated by the oppo'sitionof the several flights aswell as being fed concurrently with the agitation. 'Ihe agitation, which of course is desirable and important, is so marked that, as the retort fills with coal, even the upper surface thereof, represented by the dotted line 26, will have humps 21-21-21 alternating with depressions 28-28-28. The depressions occur approximately above the middle of the forward fiights 20 and 24.

'Iheflow of the coal may be-considered as comprising a forwardmain stream flowing horizontally into and across the lower part of the retort and effected by the forward flights, and` branch streams deflected upwardly from the main stream by the reverse flights'.

By this means the coal' fed into the retort entirely and evenly fills the retort'and moves upwardly therethrough without packing, andin a loose, constantly agitated mass which, as is' well understood by those skilled in the art, facilitates uniform and complete combustion.

My invention is not limited to the exact arrangement of the screw and hopper illustrated and described above, since, as indicatedv above, variations. in the disposal and. arrangement of the elements of the screw may be made without departing from the spirit of my` invention, or sacricing its advantages, and that the arrangementand disposition of the elements of the screw may be arrived at in accordance with the length of the retort; and all such modifications and changes which come within the scope of the appended claims are comprehended as a part of my invention.

I claim:

1,'A feed screw for feeding coal or like discrete material into a retort or the like having forwardly and rearwardly spaced end walls, comprising an axially extending shaft for projection into the retort, a main forward feeding thread flight on the shaft continuing into the retort and having a terminal forwardly of the'rearvward wall of the retort, a reverse flight Vspaced material into a retort or the like having forwardly andl rearwardly spaced walls, comprising a screw shaft projected into the retort, a main forward feeding thread flight on the shaft having a terminal rearwardly of the forward wall of the retort, a reverse flight forwardly of the terminal and continuing into a forward flight of greater axial extent than the reverse flight, and a reverse forwardly of the last named forward flight adjacent to the forward wall of the retort.

3. A feed screw for feeding coal or like discrete material into and through a retort or the like having forward and rearward spaced end walls, comprising a screw shaft projected into a lower part of the retort through the rear wall, a main forward feeding thread flight on the shaft terminating rearwardly of the forward wall, a series of supplemental forward feeding thread flights on the shaft forwardly of the main flight each preceded by a reverse thread flight of shorter axial extent than the corresponding supplemental forward flight, the main and supplemental forward flights being formed to feed material into and through the lower portion of the retort toward the forward wall in a main stream, and the reverse flights being formed to deflect material from the main stream into branch streams flowing upwardly through the retort, and a reverse thread flight on the shaft adjacent to the forward wall.

FORREST S. FRANKLAND. 

